A standard clasp knife comprises a generally planar blade pivoted on an elongated handle between an open or extended position with the plane of the blade and the longitudinal axis of the handle aligned or coinciding and a folded or closed position with the blade recessed in a pocket formed in the handle. In U.S. Pat. No. 4,083,110 of Goldin the handle is basically U-shaped and the blade pivots about an axis lying in the plane of the blade. When folded the blade is surrounded by the U-shaped handle. When extended there is, however, no system for holding the blade in place so that this knife is quite difficult and even dangerous to use.
U.S. Pat. No. 4,947,551 of Deisch pivots similarly but a catch is provided to hold the blade in the extended position. While this structure is quite a bit safer than the Goldin system, the knife is quite complex. It is therefore expensive to manufacture and is fairly bulky even when folded up. Operating the catch takes two hands, making the device inconvenient to use.
While the knife of U.S. Pat. No. 4,536,959 of Ross has a catch and is of fairly simple construction, the system for holding the blade in the extended position is not very reliable. It relies on the user tightly gripping the handle in a certain way to maintain the blade lock. It is relatively easy to inadvertently release the blade so that this system is also fairly dangerous to use.
U.S. Pat. No. 5,953,821 of Mearns works like the Goldin system with a U-shaped handle. The catch is fairly weak in this system so that the blade can be easily unlatched. In U.S. Pat. No. 2,174,947 of Barsby another such system is shown where the catch is also quite weak and could release the blade or, at the very least, allow it to wobble while cutting.